Always better value if you build it yourself (well 99% of the time there are some cheap deals out there), I build my own computers, but the question of what to get, always get the fastest CPU you can, as much ram as practicle, then the rest depends what you want to do with it, play games, word process, watch TV, burn DVD's - - lotsa questions you need to answer :0)

*CPU - AMD Athlon XP. The Intels seem to be faster than supposedly comparable AMD models, but the AMD is cheaper and better value and performance for the money
*Brand name 400 MHz DDR RAM (Kingston, Corsair)
*Graphics card - the momentum seems to be swinging to ATI graphics cards now - the latest GeForce FX, I think the cooling fans are a bit noisy - that will drive you nuts in the long run.
*Hard drive - Seagate, Western Digital - get one with 8MB cache. 120 or 160 GB drives are the best capacity per dollar at the moment. After that the prices go up more.
*Sound card - In my opinion, I've always stuck with Creative Labs - the Audigy 2 model has full DVD sound quality.
*As for the motherboard, one with the NForce2 chipset seems to be best for Athlon XP processors currently

For PC and parts prices in Melbourne - the Age newspaper's Green Guide on Thursday has a few ads from computer vendors.

I personally wouldn't touch brand name PCs like Dell etc. You will pay extra for a PC with every price shortcut possible. Whereas if you custom build your machine, you can end up with a quality machine for similar money. Most vendors will advertise the good brand name parts, and not mention the crap brand names of the parts that make up the rest of the machine.